// FIXME Demo
CombineUnions Logical Optimization
CombineUnions is a base logical optimization that FIXME.
CombineUnions is part of the Union once-executed batch in the standard batches of the Catalyst Optimizer.
CombineUnions is simply a Catalyst rule for transforming logical plans, i.e.
Executing Rule —
apply(plan: LogicalPlan): LogicalPlan